Frost pattern floor
Patterned ground (even structure bottom ) is a collective term for surface shapes with regular structures, which by the action of ground frost caused. Various geomorphological processes are responsible for the formation, but above all thermal contraction and frost lift . These can sort the soil particles. Frost pattern soils occur mainly in the periglacial zone, but can also occur outside of this in areas with intense frost effects.
There are different classifications for the very different shapes of the frost pattern floors, almost all of which are based on the classification proposed by Albert Lincoln Washburn . A distinction is first made between sorted and unsorted shapes - the sorted ones, in contrast to the unsorted ones, are sorted on the surface according to grain size and are usually surrounded by stones. In German, the term structured floor , which is also used as a synonym for frost pattern floor , is only related to the sorted frost pattern floors according to a definition by Carl Troll , the unsorted shapes are then referred to as texture floors . Within this dichotomy, a distinction is made according to shape - there are mainly stone rings , stone polygons and stone nets in predominantly flat terrain, as well as stone strips and stone garlands in sloping surfaces. The most common form in permafrost areas are ice wedge polygons , a special form of unsorted polygons (polygons).
On Mars , too , high-resolution images show patterns that correspond to the frost pattern soils on Earth, especially in polygonal form. In the areas where such patterns can be seen, ground ice has been detected, and some of these structures are otherwise very similar to those on Earth.
Classification
The classification proposed by Washburn in 1956 is based on the appearance of the frost pattern floors and deliberately not on the development process that leads to this pattern. The division is also not in the pedological sense . For this reason it is detailed or slightly modified in various ways.
Assorted frost pattern floors
Assorted frost pattern soils, for which the term structured soils is also used, have a sorted grain size spectrum. The shapes are structured by larger stones, with finer material inside the cells. The dimensions of these structures range from less than 20 centimeters to large shapes with a diameter of several meters.
The main forms are as follows:
- Assorted stone rings
- The pattern of this form of the structured floor is similar in numerous directions, the structures are almost circular. The sorted appearance usually results from the fact that the finer material is framed by stones. Sorted rings can appear individually or in groups. The diameter is usually between half a meter and three meters. Flat stones are often on edge. There can also be stones in the central area of the stone ring.
- Assorted stone polygons
- This shape is similar to the sorted circles, the pattern is similar in several directions, but the result is polygon-like structures. The patterns can extend over a fairly large area, mostly they are located in almost flat terrain. The diameter of the polygon-like cells can be between 10 centimeters and 10 meters, smaller polygons inside the pattern are often surrounded by larger ones further outside.
- Assorted stone nets
- In this shape, too, the pattern is similar in several directions, but the resulting shapes are neither circular nor polygonal. The diameter of the individual cells is between half a meter and ten meters. With a larger diameter, the surrounding stones are usually larger.
- Assorted stone strips
- These form a strip-like sequence of stones and finer material. Such patterns can occur from a slope of 3 °, the stripes run along the fall line and can extend over several hundred meters. Stone strips often represent a slope-side continuation of sorted polygons or nets.
- Assorted stone steps or stone garlands
- This is a step-like pattern that occurs on a slight slope, with finer-grained material at the lower edge often being framed by stones like a tongue. The slope is typically between 5 ° and 15 °. It can be assumed that sorted steps do not represent an independent pattern, but correspond to sorted circles or sorted polygons influenced by the slope. Some sorted stone levels clearly represent an intermediate level between sorted stone polygons and sorted stone strips.
Unsorted frost pattern floors
Unsorted frost pattern floors, also known as texture floors , are not sorted according to grain size. They have a homogeneous, mostly fine-grained substrate. The pattern-forming role of the stones in the sorted frost pattern soils is often played by the vegetation in the unsorted ones.
In the case of unsorted frost pattern soils, a distinction is mainly made between the following:
- Unsorted stone rings
- As with the sorted stone rings, the pattern is similar in numerous directions, the structures are almost circular. In contrast to the assorted counterpart, there is no border made of stones, rather vegetation often forms this border. The diameter of the rings is usually between half a meter and three meters. Some forms of unsorted rings are also called " frost boils ".
- Unsorted stone polygons
- In terms of the pattern, these correspond to the sorted counterpart, as with the circles, the unsorted variant is not framed by stones. This pattern often extends over large areas, mostly in flat terrain, but unsorted polygons are also possible on slopes, even up to a slope of 30 °. A distinction is made between micro and macro shapes, the former have a diameter of between 5 centimeters and about a meter, the latter can be over 100 meters. If the vegetation is sparse, it will typically concentrate around the framing furrows, emphasizing the pattern. Ice wedge polygons are a special form in permafrost areas. In this macro shape, the structure is formed by ice wedges . The diameter can be up to 150 meters, on average it is 10 to 40 meters. Mainly triangular to hexagonal shapes are formed in the plane.
- Unsorted stone nets
- As with unsorted stone rings and stone polygons, the pattern is similar in several directions, but the resulting shapes are neither circular nor polygonal. The diameters of the individual cells are between half a meter and ten meters. As with the unsorted polygons, the pattern can be emphasized by vegetation. Various forms of hummocks fall into this category.
- Unsorted stone strips
- As with the sorted counterparts, the stripes run down the slope, but in this case the stripe pattern is formed by a change in vegetation density. The strips can be several 100 meters long. Sometimes strips of the same width alternate with and without vegetation, in other cases there are 30 to 60 centimeters wide overgrown strips that are separated by 3 to 4.5 meters wide strips without vegetation. Unsorted strip shapes occur on slopes between 3 ° and 6 ° and can be the slope-side continuation of unsorted polygons or networks.
- Unsorted steps
- Like the sorted counterpart, these occur on slopes, with the steps being framed by vegetation instead of stone garlands. The incline is usually between 5 ° and 15 °. It is assumed that unsorted steps correspond in principle to unsorted networks or polygons, the development of which is influenced by the slope.
Emergence
There are partly different development processes that lead to the different forms of frost pattern soils. This seems to apply particularly to the unsorted forms, but various causes are assumed for the unsorted stone rings. Today, there is not a generally accepted explanation for all forms.
Frost pattern soils are very common in areas with permafrost , where the main cause is thermal contraction and the formation of ice wedges . But repeated freezing and thawing processes also play a role. Processes such as differentiating frost lift , cryoturbation , cryostatic pressure and diapiral displacement of water-saturated material are involved, as well as solifluction on slopes .
The trigger for the formation of the ice wedge polygons , which are common in permafrost areas, is thermal contraction. The ground tears open as a result of low winter temperatures and the crevices are filled with snow, frost, re-freezing water or other material. With the higher summer temperatures these cracks close again. In the following winter, they tear open again at the same point, as the predominantly ice filling of the former crevices can withstand less tension than the frozen ground, which intensifies the process. The increase in volume when water freezes is not decisive here, as can also be seen from the fact that there are polygons in very dry areas whose crevices are filled exclusively with sand. Using numerical models, it can be understood that the contraction cracks form polygonal patterns, the shape and size of which mainly depends on the nature of the soil and the temperature differences. More decisive than the mean temperatures, however, are irregular rapid drops in temperature. This makes it difficult to draw conclusions about past climatic developments from the shape and size of the patterns.
In contrast to the ice wedge polygons, repeated freezing and thawing processes play a decisive role in the assorted frost pattern floors. In a work published in 2003 it is demonstrated that the different forms of sorted frost pattern soils can be reproduced by means of a numerical model if principles of self-organization are applied. The simulation model was only influenced by two parameters, on the one hand the slope and on the other hand the degree of "crowding" by neighboring cells. The formation process assumed in this simulation model can be divided into several phases: First, the formation of ice lenses and the resulting frost lift promotes the stones in the opposite direction to the frost impact, i.e. tending to upward, which is also known as freezing . An isolated stone on the surface of the ground now represents an unstable condition that is prone to faults, since the frost stroke at the soil-stone boundary has an inconsistent effect - due to the different moisture levels below and next to the stone. This results in sorting and the formation of separate stone and floor areas. Due to the “pressure” that the expanding floor area continues to exert on the stone area, the stone area is now stretched lengthways. Depending on the degree of competition from neighboring cells, the different shapes are created, with strong competition polygonal shapes arise, with less circular ones. If the slope is steep, there will be streaks.
Fossil frost pattern soils
Frost pattern soils that have arisen in the past and where the climatic conditions of the present no longer allow the creation or further development of such formations are referred to as fossil - in contrast to the active or recent frost pattern soils. Examples of this are inactive ice wedge polygons that can be found in former permafrost areas. If the thawing ice has been replaced by other filler material, one speaks of ice wedge pseudomorphoses . In some cases, the polygonal pattern former ice wedges reflect in the vegetation, for example in the form of crop marks in cornfields. Some of these structures can be found in the mid-latitudes , especially in meltwater depressions and areas with debris from the Saale Ice Age . Usually only relatively young structures can be seen from the air, as older ones are covered by sediments. Other forms of frost pattern soils are often still recognizable as areas with former cryoturbation , but it is often not clear which form they originally corresponded to. Assorted frost pattern soils are rarely found in fossil form, possibly because they are not recognized as such.
Polygon-like structures on Mars
Polygonal structures in the great northern plain have already been identified in pictures from the Viking missions of the 1970s . The diameter of the polygons, which is between two and ten kilometers, almost excludes the possibility of an analogy to the terrestrial periglacial phenomena - tectonic disturbances were assumed to be the cause of these forms. With the high-resolution images of the Mars Global Surveyor and the Mars Reconnaissance Orbiter , structures became visible that seem far more to resemble the frost pattern soils on earth. If you categorize these in terms of shape and cell size, the result for many of these categories is that the respective shapes can be found in corresponding latitudes on the northern and southern hemisphere - which indicates a climatic connection. Ground ice was also detected in these areas with the neutron spectrometer . It is believed that many of these polygons, similar to the ice wedge polygons on Earth, are formed by thermal contraction of frozen ground. It is unclear whether and to what extent repeated freezing and thawing processes are also involved in some cases. This would be particularly conceivable in the past, since the inclination of the Mars axis - due to the lack of stabilization by a large moon - is subject to far greater fluctuations than that of the Earth's axis. In the last 10 million years there have also been inclinations of up to 50 °, which resulted in extreme differences between summer and winter temperatures.
In the area near the northern polar region in which the Phoenix landed in 2008, there are polygons with a diameter of three to six meters, as are common in the northern plain. It is assumed for these that they are formed by thermal contraction like the ice wedge polygons on Earth. It is assumed that they are active as the structures are quite pronounced. Similar to the polygons to be found in the Antarctic dry valleys, the crevices are mainly filled with sand and rubble. According to calculations of a numerical model , polygons of this size result if a layer two to six centimeters thick with ground ice is assumed. If it reached deeper, the polygons would have to be larger. In these widths there are also larger polygons with diameters of 20 to 25 meters. These can be explained in the same way if one assumes an earlier formation of these polygons, at a time of more extreme climates with a greater inclination of the Martian axis than the bottom ice layer was ten to twelve centimeters thick. There are also regularly arranged clusters of rocks and rubble, which result in a pattern with dimensions roughly corresponding to the polygons. It is believed that this sort of material is related to the evolution of the polygons. In contrast to the earthly sorted frost pattern soils, this sort of material is obviously neither due to freezing and thawing processes nor to frost lift.
See also
literature
- Hugh M. French: The Periglacial Environment. 3rd edition, Wiley-Verlag, Chichester 2007, ISBN 0-470-86588-1 (English)
- Albert L. Washburn: Geocryology. Edward Arnold Publishers, London 1979, ISBN 0-7131-6119-1 (English)
- Albert L. Washburn: Classification of patterned ground and review of suggested origins. In: Bulletin of the Geological Society of America. Volume 67, 1956, pp. 823-865 ( abstract , English)
Web links
- Lund University: Periglacial Environments 3, Patterned Ground. Photos of different types of frost pattern floors (PDF, 10.1 MB)
Individual evidence
- ↑ a b c d Ronald P. Daanen, Debasmita Misra, Anita M. Thompson: Frozen Soil Hydrology. In: Vijay P. Singh, Pratap Singh, Umesh K. Haritashya (Eds.): Encyclopedia of Snow, Ice and Glaciers. Springer, Dordrecht 2011, pp. 306-311, ISBN 978-90-481-2641-5
- ↑ a b geodz.com: Frost pattern floor . . Retrieved May 20, 2013
- ^ A b Carol F. Sawyer: Classics Revisited: Washburn's Classification of Patterned. Ground and Review of Suggested Origins. In: Progress in Physical Geography. Volume 36, pp. 440–448, 2012 ( doi: 10.1177 / 0309133312438909 )
- ^ A b Nicolas Mangold: High latitude patterned grounds on Mars: Classification, distribution and climatic control. In: Icarus. Volume 174, pp. 336–359, 2005 ( online ( memento of the original from April 29, 2014 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice . ; PDF; 2.6 MB)
- ^ Herbert Louis, Klaus Fischer: Allgemeine Geomorphologie. 4th edition, pp. 160–163, Verlag Walter de Gruyter, Berlin 1979, ISBN 3-11-007103-7 ( Google books )
- ^ JV Drew, JCF Tedrow: Arctic soil classification and patterned ground. In Arctic. Volume 15, pp. 109–116, 1962 ( online ( memento of the original dated August 30, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice . )
- ↑ Thierry Feuillet, Denis Mercier, Armelle Decaulne, Etienne Cossart: Classification of sorted patterned ground areas based on their environmental characteristics (Skagafjörður, Northern Iceland). In: Geomorphology. Volume 139–140, pp. 577–587, 2012 ( online ; PDF; 4.1 MB)
- ↑ a b c National Snow and Ice Data Center, Frozen Ground Data Center: English Language Glossary of Permafrost and Related Ground-Ice Terms. ( Memento of the original from December 26, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved May 22, 2013
- ↑ Martha K. Raynolds et al .: A map analysis of patterned-ground along a North American Arctic Transect. In: Journal of Geophysical Research. Volume 113, G03S03, 2008 ( doi: 10.1029 / 2007JG000512 )
- ↑ a b Julia A. Jackson, James P. Mehl, Klaus KE. Neuendorf: Glossary of geology. Springer Verlag, Berlin 2005, ISBN 0-922152-76-4 ( Google books )
- ^ LJ Plug, BT Werner: A numerical model for the organization of ice-wedge networks. In: Permafrost Seventh International Conference Proceedings. Volume 55, pp. 897–902, 1998 ( online ; PDF; 1.1 MB)
- ^ LJ Plug, BT Werner: Nonlinear dynamics of ice-wedge networks and resulting sensitivity. In: Nature. Volume 417, pp. 929–932, 2002 ( online ( memento of the original from October 18, 2012 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice . ; PDF; 476 kB)
- ^ MA Kessler, BT Werner: Self-Organization of Sorted Patterned Ground. In: Science. Volume 299, pp. 380-383, 2003 ( summary )
- ↑ French: The Periglacial Environment. Pp. 310-315, see literature
- ↑ John Card: Pleistocene periglacial conditions and geomorphology in north central Europe. In: John Boardman (Ed.): Periglacial Processes and Landforms in Britain and Ireland. Cambridge University Press, Cambridge 1987, ISBN 978-0-521-16912-7 ( Google books )
- ↑ Michael T. Mellon et al .: A map analysis of patterned-ground along a North American Arctic Transect. In: Journal of Geophysical Research. Volume 113, E00A23, 2008 ( doi: 10.1029 / 2007JE003039 )
- ↑ Joseph S. Levy, David R. Marchant, James W. Head: Thermal contraction crack polygons on Mars: A synthesis from HiRISE, Phoenix, and terrestrial analog studies. In: Icarus. Volume 206, pp. 229-252, 2010 ( online ( memento of the original dated April 29, 2014 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice . ; PDF; 3.4 MB)
